Magnetron type seismometer



Charles G. Cruznn, lartlesville, Gide., assigner nilips Petroleum Company, a corporation ol iteiarvare application March l2, HSL Seriai No. lr

This invention relates to seismorneters. in one specic aspect, it relates to a seismorneter wherein relative translational or rotational movement of a support r tive to an inertia body varies the strength of a magnetic field controlling the ow of electrons through an electron tube,

Heretofore, many types ci seisruometers have been proposed in which rninute ground movements produce relative movement between a support or casing and an inertia body, such relative movement causing a change in a parameter ot an electrical syste i and thereby producing an electrical output representative of the seismic waves incident upon the seisrnorneter. insofar as l am aware, no one has previously applied the principles of the magnetron type ci vron tub-e to transforming the seismic waves into eiecmcal voltages or currents representative thereof.

it is an object ot my invention to provide a new and improved type of seisrnometer.

lt is a further object ot` the invention to provide a practical embodiment of a seismometer utilizing the prin ciples o: the magnetron type of electron tube.

lt is a further object to provide a seisinometer which is sensitive, reliable, and sutliciently rugged as to withstand rough usage in the eld.

Various other objects, advantages 'features ot' the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure l is a vertical sectional view, partially in elevation, of a seisrnorneter constructed in accordance with this invention;

Figure 2 is a top view of the seisrnorneter shown by Figure l;

Figure 3 is diagrammatic view illustrating the principle of'operation and a suitable electrical circuit for use wth the scismometer of Figures 1 and 2.

Figure 4 is a diagrammatic View of a modified for sL of seisrnorneter with a suitable electrical circuit therefor:

Figure 5 is top view of a further modification of the invention; and

Figure 6 is a perspective view of a further modification of the invention.

Referring now to the drawings in detail and particularly to Figures i and 2, the seisrnonieter comprises a support or casing having a base lil. Secured to the casing id is permanent magnet i2 of the bar type, the respective ends of magnet 12 being embraced by the legs of a pair of horseshoe-shaped ux guides E3 and M which are formed from magnetic material. An electron tube l5 is suitably secured within the upper or curved portions of the flux guides 13 and liti. The tube 1S is preferably of the diode type and has a cylindrical anode i6, ure 3, and an axial cathode i7 which is illustrated as being of the directly heated type although an indirectly heated type cathode rnay be used, if esired. lt will be apparent that the magnet 12 operating in conjunction with 4linx guides 13 and -fi establishes a magnetic field directed longitudinally between the anode and cathode ot the tube 1S, as is indicated by the dotted lines i8 of Figure 3.

An inertia body 2d, preferably consisting of a cylir cal piece of magnetic material, is secured to the casing ill by a spring suspension 2i, this suspension including a thin flat iear spring suitably secured at both enos to the casing it? Seismic waves incident upon the unit cause t. e casing to be shifted vertic v relative to inertia body it' with 'th result that the tube is moved toward or away from th magnetic inertia body 2d.

The electrical circuit associated with the tube 15 includes a filament battery Z5 and filament voltage supply leads 21S an 27. Lead 27 also constitutes the cathode lead and is connected through a battery a load resistance 29, and a lead Eil to the anode in. En this manner, operating potentials are supplied to the electrodes o the tube. The input circuit of aniplier 3i is connected across the resistance one input lead being connected through a condenser 32 to lead and the other input lead 35 being connected to the junction between resistance 29 and battery The output of an liti r 3i is fed to an indicating device 345 which in the seis;m

res the intensity ie waves in the manner hereinafter described. it will nderstood that, by the terni indicator, I intend to include an indicating meter, a recorder, or any other suitable device for producing an indication representative of the current ilow in the anode-cathode circuit of tubo 15. if desired the base l may be hollow, and of sutiicient size as to accommodate the battery 25 in the operation of the seismometer, stated, relative movement between the casing and inertia body produced by seismic waves causes tube i5 to move toward or away from inertia body Fr/'hen inertia body 2li occupies a position reinote 'from the tube, it does not interfere with the magnetic `Field produced by the linx g es i3, id and the magnet ft2. As a re t, a maximum field exists between the anode the cathode with the result that the plate current through the tube is a minimum. When the inertia body is positioned close to the tube, as indicated by the dotted lines of Figure 3, the inertia body 2@ tends to pull the stray linx which surrounds it so as to pass through it since it provides a path of low reluctance for such tiux. Consequently, the intensity of the magnetic field between the anode and the cathode is reduced with the result that the plate current is increased. Thus, the variations in anode current ilowing through the tube l5 are representative of the seismic waves incident upon the seisrnonieter. These current variations are arnplitied by unit 3l and the amplifie-d current is fed to indicator 3d.

ln the modification of the invention shown by Figure 4, two similar assemblies are provided, one of which is positioned above the inertia body 2d and the other ot which is positioned below the inertia body 2G. These assemblies include tubes i550, 5.5!), lux guides i3d, 13b and lila, Mb corresponding to the similarly numbered elements of Figures l and 2. it will be understood that the fiux gui-:les have permanent magnets associated therewith, that the inertia body is suspended from a casing, and that the magnetic assembly is mounted upon the casing in the manner described in connection with Figures l and 2. The tubes have anodes Een, leb, larnents or cathodes Yin, r) t i output leads 26u, 261); 27a, ib; and 3de', 3b corresponding to the similarly num bered elements in Figures l and 2. "the leads 26a, 2615 are both connected to the positive terminal oi a filament battery 35, the negative terminal of which is connected to the junction between leads 27o and fb. Also connected to this junction is the negative terminal of a battery 37, the positive terminal of which is connected to the junction between the resistances 3 and Lib which, in turn, are connected to the respective leads Siti-tz and Sill).

The push-pull amplifier 41 has its input circuits connected through coupling condensers 42, 43 and ground at 44 to lead 36a, lead Stib, and the junction between resistances 39, 4f?, respectively. The output of push-pull amplifier 41 is fed to an indicating device 45.

In the operation of the circuit of Figure 4, upward movement of the assemblies causes the inertia body 2t) to be positioned closer to tube 15b and further away from tube 15a. As a result, the anode current in tube 15b is increased and the anode current in tube 15a is decreased. Downward movement of the assemblies produces an opposite effect. That is, the anode current through tube 15a is increased while the anode current through tube 15b is decreased. These out of phase current variations are reinforced by the action of push-pull amplifier 41 and produce variations at indicator 45 which are representative of the seismic Waves incident upon the seismometer.

In the modification of the invention shown by Figure 5, two assemblies are provided which are similar to those described in connection with Figure 4, the output leads of the tubes being connected to a suitable amplifier circuit of the same type and in the same manner as described in connection with that figure. ln the modification, however, the inertia body includes a rod 46 carrying an inertia member 47 of magnetic material which is positioned at one end of the rod adjacent tube 15a and a second inertia member 48 of magnetic material which is positioned at the other end of rod 46 adjacent tube 15b. The central portion of rod 46 is secured to the center of a torsion wire 49 having its ends suitably secured to the casing 10. In the modification shown by this figure, relative translational movement between the casing and inertia body has no effect. However, relative rotational movement between the casing and inertia body produces an electrical output representative thereof. Thus, rotational movement of the casing in a clockwise direction, as viewed from the righthand side of Figure 5, causes tube b to move closer to inertia body 48 while tube 15a moves away from inertia body 47. As a result, the plate current in tube 15b is increased while the plate current through tube 15a is decreased. Rotation of the casing relative to the inertia body in the opposite direction produces an opposite effect resulting in an increase in the plate current of tube 15a and a decrease in the plate current of tube 15b. As a result, the currents amplified and combined in push-pull amplifier 41 and indicated by unit 45 are representative of the rotational waves incident upon the seismometer.

In the modification of the invention shown by Figure 6, a cylindrical casing 55 is provided which incorporates a hollow base 56 suitable for housing the filament battery of the tube. A tube 15C is supported in a horizontal position by suitable brackets 57 and 58. Encircling the tube 15C and positioned adjacent the ends thereof are a pair of annular' permanent magnets 59 and 60 so arranged that the inner facing surfaces thereof are of opposite polarity. The tube 15C is connected in a circuit similar to that shown by Figure 3.

An inertia body 62 of magnetic material is suspended from the casing by a flat leaf spring 63 which includes a central portion 64 supporting the inertia body together with three curved arms 65 which extend radially outward toward and are secured to the casing 55, the outer ends of the arms fitting within slot 66 in the casing. The permanent magnet produces a eld similar to that shown in Figure 3, and seismic waves incident upon the unit cause the casing to be shifted vertically relative to the inertia body 62, thereby producing a current representative of the seismic waves in the manner described in connection with Figures 1 and 2.

While the invention has been described in connection with a present, perferred embodiment thereof, it is to be understood that this description is illustrative only and is not intended to limit the invention, the scope of which is defined by the appended claims.

1 claim:

1. A seismometer comprising, in combination, a support adapted to be moved by seismic waves, an inertia body including a member of magnetic material, an electron tube rigidly secured to said support, said tube having an elongated axial anode and cathode, means for supplying operating potentials to the electrodes of said tube, means for establishing a magnetic field between said anode and said cathode, and a spring suspension connecting said support and said inertia body and arranged to produce relative movement between said member of magnetic material and said support along a line perpendicular to the axis of said anode and cathode in response to seismic waves incident on said support, thereby to vary said magnetic field and the current in the anodecathode circuit of said tube.

2. A seismometer in accordance with claim 1 in which the spring suspension is a leaf spring having both ends thereof secured to the support and disposed parallel to said axis, the inertia body being a disk of magnetic material secured to said leaf spring.

3. A seismometer in accordance with claim 1 in which a second tube having an elongated axial anode and cathode is rigidly secured to the support, and the relative movement between said member of magnetic material and said support is along a line perpendicular to the axis of the anode and cathode of both tubes.

4. A seismometer in accordance with claim 1 wherein the spring suspension is a torsion wire having both ends secured to said support, and wherein the relative movement between the magnetic member and support is angular relative movement.

5. A seismometer comprising, in combination, a support adapted to be moved by seismic waves, an inertia body including a member of magnetic material, an electrode tube rigidly secured to said support, said tube having an axially-extending cathode positioned within a generally cylindrical anode, means for supplying operating potentials to the electrodes of said tube, means for establishing a longitudinally-oriented field between said anode and said cathode, and a spring suspension connecting said support and said inertia body and arranged to produce relative movement between said member of magnetic material and said support along a line perpendicular to the axis of said anode and cathode in response to seismic waves incident on said support, thereby to vary said magnetic field and the current in the anode-cathode circuit of said tube.

References Cited in the le of this patent UNITED STATES PATENTS 1,673,681 Hull et al June 12, 1928 1,784,415 Benioff Dec. 9, 1930 1,864,214 Petty June 21, 1932 2,219,745 Linder Oct. 29, 1940 2,338,732 Nosker Ian. 11, 1944 2,372,056 Broding Mar. 20, 1945 2,390,187 Sharpe Dec. 4, 1945 2,476,611 Linder July 19, 1949 2,487,029 Piety Nov. 1, 1949 2,587,481 Kaehni et al Feb. 26, 1952 FOREGN PATENTS 798,715 France Mar. 11, 1936 

